Specification of the new core safety measures

The ESFR-SMART core description has been established in several steps on the basis of ESFR-WH core design proposed for the EURATOM CP-ESFR project and experiences gained in EURATOM ESNII+ project. The axial arrangement above the core (Na plenum and absorber) of CP-ESFR was adopted. For further Na void effect reduction, it was proposed to reduce the inner core fissile height: following late CP-ESFR and ESNII+ studies. Unlike ESNII+, an option was considered to keep the upper fissile boundaries at similar axial locations in the inner and outer cores. The ESFR-SMART core includes extra fuel subassemblies at the outer core periphery in order to compensate the inner fissile height reduction. It was also aimed to use the same fuel enrichments in the inner and outer cores, if possible. The corium discharge tubes were included: at the central position, between inner and outer cores, and at the core periphery. The number of DSD locations, including those for passive safety devices, was increased. The axial part between the fissile region and lower gas plenum was proposed to be a combination of the fertile lower blanket and steel reflector below: to reduce the sodium void effect, but prevent breeding. The fissile and fertile heights and single fissile enrichment were finally chosen on the basis of fine optimization studies. A 6-batch fuel reloading scheme was proposed, instead of a 5-batch one in CP-ESFR. The core is surrounded by 2 rings of steel reflector and 1 ring of absorber subassemblies. Outside of absorber there are locations for spent fuel subassemblies, including 3 inner and 3 outer core batches. In the new ESFRSMART core, the calculated void effect is significantly reduced: to a value well below 1$ at the end of cycle. In the following, core specifications are given, which can be most easily used for deterministic neutronics codes such as ERANOS. These specifications contain dimensions and nuclear densities at the room temperature, temperatures related to operating conditions, and tables for thermal expansion. To facilitate model preparations and calculations with Monte-Carlo codes, an additional dataset for a simplified core description at operating conditions is also provided. The appendix contains the EDF report on details of the core design optimization with the SDDS multi-physics and multi-objective method.